1.1 本实践提供了一个框架，用于评估反光膜在夜间驾驶条件下的性能，而无需通过一组表示常见用例的标志查看场景进行现场评估。通过比较挡板提供的亮度与驾驶员在每个场景中所需的亮度来评估特定挡板的性能。这种比较用“性能指数”表示，该指数衡量在每种情况下提供给驾驶员的亮度满足其需求的程度。比较不同挡板的性能指标值，使用户可以预测在安装的标志上使用这些挡板时夜间反光性能的差异。 1.2 驾驶员需要的数据基于具有正对比度的文字标志（而非符号标志）（标志文字比其背景亮），并且假设前照灯照明为近光；因此，性能指标仅适用于在近光前照灯照明下查看的文字标志。 1.3 单位- 以国际单位制或英寸-磅单位表示的数值应单独视为标准值。每个系统中规定的值可能不是精确的等效值；因此，每个系统应相互独立使用。将两个系统的值合并可能会导致不符合标准。 1.4 本标准并非旨在解决与其使用相关的所有安全问题（如有）。本标准的用户有责任在使用前制定适当的安全、健康和环境实践，并确定监管限制的适用性。 1.5 本国际标准是根据世界贸易组织技术性贸易壁垒（TBT）委员会发布的《关于制定国际标准、指南和建议的原则的决定》中确立的国际公认标准化原则制定的。 ====意义和用途====== 5.1 反光膜通常用于在车辆前照灯照明下提高夜间交通标志的可见度和易读性。本标准提供了一个程序，用于根据预定义道路场景的总体平均性能指数评估道路标志中使用的标志挡板的夜间反光性能。 5.2 在不进行现场工作的情况下，描述夜间标志亮度供应和驾驶员亮度需求之间关系的程序有助于交通工程师和负责指定公路施工材料和维护道路安全的运输机构就标志上反光膜的性能作出知情决定。 该程序要求根据实践对反光膜的反光性能进行全面测量 E809 在广泛的角度上。 5.3 各种反光膜可用于交通标志。逆反射系数通常针对一组标准角度组合进行测量，部分用于证明符合规范或标准。然而，虽然一些标准角度集上的逆反射系数可以提供有关挡板逆反射的一般概念，并有助于证明符合标准，但需要进行更全面的分析，以确定挡板在一般情况下或在特定使用中为驾驶员服务的程度- 案例。在现实世界中，不同车辆的驾驶员在观看大量标志时，会遇到比标准角度集中捕捉到的角度组合复杂得多的角度组合。此外，驾驶员观察亮度，亮度不仅受逆反射系数的影响，还受前照灯照明、车辆到标志的距离和光衰减等因素的影响。 5.4 这种做法利用了一组驾驶员标志查看场景。当与相应几何形状处的逆反射系数相结合时，计算驾驶员观察到的亮度。 还为用户列出了驾驶员对不同百分比的亮度要求。将标志的亮度供应与驾驶员的亮度需求进行比较，可以评估每个场景中的预期“性能指数”。 5.5 驾驶员亮度需求的数据代表了美国55岁或55岁以上合法驾驶员子集的视觉表现，可能不代表整个驾驶员群体的视觉表现。

1.1 This practice provides a framework to evaluate retroreflective sheeting performance in nighttime driving conditions without a need for field evaluations through a set of sign viewing scenarios representing common use-cases. The evaluation of performance of a specific sheeting is achieved by comparing the luminance provided by a sheeting to the luminance needed by drivers in each scenario. This comparison is expressed in terms of a “Performance Index,” which is a measure for how well the luminance provided to the driver meets their needs, in each of the scenarios. Comparison of the performance index values for different sheeting allows the user to predict differences in nighttime retroreflective performance when those sheeting are used on installed signs. 1.2 The driver-needs data is based on textual signs (not on symbolic signs) with positive contrast (sign text being brighter than its background), and the headlamp illumination is assumed to be low-beams; therefore, performance index is applicable only to textual signs viewed under low-beam headlamp illumination. 1.3 Units— The values stated in either SI units or inch-pound units are to be regarded separately as standard. The value stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in nonconformance with the standard. 1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. ====== Significance And Use ====== 5.1 Retroreflective sheeting is commonly used to improve the nighttime visibility and legibility of traffic signs under vehicle headlight illumination. This standard provides a procedure for evaluating the nighttime retroreflective performance of sign sheeting used in roadway signing in terms of an overall average performance index for predefined road scenarios. 5.2 A procedure to characterize the relationship between sign luminance supply and driver luminance demand at night without conducting field work helps traffic engineers and transportation agencies responsible for specifying highway construction materials and maintaining roadway safety in making informed decisions about the performance of retroreflective sheeting on the signs. The procedure requires the comprehensive measurement of the retroreflective properties of a sheeting according to Practice E809 over a wide range of angles. 5.3 A variety of retroreflective sheeting is available for use on traffic signs. Coefficients of retroreflection are typically measured for a standard set of angle combinations and are used, in part, to certify conformance to a specification or standard. However, while coefficients of retroreflection on some standard angle sets can provide a general idea about a sheeting’s retroreflectivity and help certify conformance to a standard, a more comprehensive analysis is needed to determine how well a sheeting is expected to serve drivers in general, or in specific use-cases. Drivers of different vehicles viewing a multitude of signs in the real world experience a much more complex set of angular combinations than those captured in the standard angle sets. Furthermore, drivers observe luminance, which is affected by not only the coefficient of retroreflection, but also by headlight illumination, distance from the vehicle to the sign, and light attenuation, among other factors. 5.4 This practice utilizes a set of driver sign viewing scenarios. When combined with the coefficients of retroreflection at the corresponding geometry, the luminance as observed by the driver is calculated. The luminance requirements of the driver for varying percentiles are also tabulated for the user. Comparing the luminance supply from the sign with the luminance demand of drivers provides an assessment of the expected “performance index” in each scenario. 5.5 The data on the luminance needs of the driver represents the visual performance of a subset of legal drivers in the United States of 55 years of age or older and may not represent the visual performance of the entire driver demographics.